We propose to combine the powerful tools of recombinant DNA technology and electron microscopic visualization of transcription in order to probe some mechanisms of eukaryotic gene regulation. We will inject various cloned genes into Xenopus oocyte nuclei, incubate the oocytes, prepare the nuclei for the EM via Miller-type spreads and analyze the transcriptional capabilities of these recombinant molecules. Where appropriate we will rearrange and/or alter various sequences of the DNA before injection to ask specific questions about the sequences required for normal initiation, termination and promoter functions. We will also test hypothesis concerning (1) the possible promoter function of "Bam islands" in Xenopus rDNA; (2) the formation of "active" rDNA chromatin; (3) the molecular basis for nucleolar dominance between two species of Xenopus; (4) the function of a Xenopus vitellogenin gene when it is not normally expressed in the oocyte; and (5) what portions of insert-containing Drosophila ribosomal genes are recognizable for their apparently inactive state.